Lower leg prosthesis – what about it?

With condyles we are talking about bony parts of the knee joint at the lower end of the thigh bone, which are responsible for a combined rolling and sliding movement on the articular surface of the head of the tibia. KBM (Kondyl Bettung Münster / condyle bedding Münster) is a shaft embedding method that encloses the condyles. In Kondyl Bettung Munster systems, the inner and outer shafts are locked by an enclosure over the condyle.

To put on the lower leg prosthesis, the stump is first wrapped with a skin protection stocking and slightly pre-compressed. The soft tissues are thus fixed and prepared for the prosthesis. Through a slot at the end of the soft-wall inner socket, the stump is pulled into the inner socket with the aid of a Perlon tube.

Subsequent adjustments following shape changes can be made quickly with these systems. This means that any volume fluctuations can be easily adjusted with compensation socks. The soft-wall inner socket can be narrowed in the same way.

In particular, condylar bedding systems show their strengths in initial treatments and in atrophic stump conditions. The loads on the end of the stump are minimized.

Silicone is a very popular liner material. It is available in different versions and shore hardnesses. The silicone liner ensures that the prosthesis remains firmly attached to the lower leg. It also holds the stump evenly and has skin-care and protective properties.

In liner systems with distal locking, the silicone liner is pushed onto the stump like a second skin. For a secure hold, it is then secured inside the prosthesis shaft with a lock. This lock is called a retainer. The retainer pin attached to the liner snaps into the counterpart fastened in the shaft. This creates a firm connection between the amputation stump and the prosthesis. A major advantage of distal retainers is the ease of use of the system.

Vacuum systems create a vacuum between the liner and the shaft. From a biomechanical point of view, vacuum systems offer decisive advantages in terms of the fixation of the prosthesis shaft to the stump. The adhesive principle of negative pressure is distributed over the entire surface, which is sealed airtight, instead of being selectively distributed over a small area on the stump. This means that the weight forces of the prosthesis are transferred to the stump much more efficiently.

Furthermore, negative pressure can be built up passively or actively. In the active variant, the air is transported out of the shaft by technical aids. Many users report better feedback from the prosthesis in the event of uneven floors, for example. Studies have shown that an active vacuum system has a positive effect on dull blood flow and volume fluctuations.

We use two different types of vacuum systems:

• Liner systems with knee caps

• Liner systems with sealing lip

Liner systems with knee caps:

The knee cap is applied over the shaft up to the thigh. It is necessary to build up and seal off the vacuum. The vacuum created between the knee cap and the end of the liner acts over the entire surface of the stump. Consequently, the core also absorbs the weight force of the prosthesis over the entire area, which in turn reduces the local load.

The liners are offered as bedding liners in all different materials such as silicone, TPE and PUR. Here too, special situations can be addressed with individual or pre-assembled compensation.

Liner systems with sealing lips:

In recent years, silicone liners with sealing lip systems in different designs have established themselves. These systems also take advantage of vacuum. However, the technique for putting on this type of liner is difficult. As a rule, users are dependent on an alcohol-based aid for putting on the orthosis. It ensures that the adhesion force is kept low when pushing onto the stump and when sliding into the shaft.

Liner systems with sealing lips offer a maximum build-up height for long stump treatments in order to be able to mount active or high-build-up fitting parts under the shaft. The wearing comfort is generally very high, as there is no need for additional materials above the knee joint.